/*
   *  fs/anon_inodes.c
   *
   *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
   *
   *  Thanks to Arnd Bergmann for code review and suggestions.
   *  More changes for Thomas Gleixner suggestions.
   *
   */
  
  #include <linux/file.h>
  #include <linux/poll.h>
  #include <linux/slab.h>
  #include <linux/init.h>
  #include <linux/fs.h>
  #include <linux/mount.h>
  #include <linux/module.h>
  #include <linux/kernel.h>
  #include <linux/magic.h>
  #include <linux/anon_inodes.h>
  
  #include <asm/uaccess.h>
  
  static struct vfsmount *anon_inode_mnt __read_mostly;
  static struct inode *anon_inode_inode;
  static const struct file_operations anon_inode_fops;
  
  static int anon_inodefs_get_sb(struct file_system_type *fs_type, int flags,
  			       const char *dev_name, void *data,
  			       struct vfsmount *mnt)
  {
  	return get_sb_pseudo(fs_type, "anon_inode:", NULL, ANON_INODE_FS_MAGIC,
  			     mnt);
  }
  
  static int anon_inodefs_delete_dentry(struct dentry *dentry)
  {
  	/*
  	 * We faked vfs to believe the dentry was hashed when we created it.
  	 * Now we restore the flag so that dput() will work correctly.
  	 */
  	dentry->d_flags |= DCACHE_UNHASHED;
  	return 1;
  }
  
  static struct file_system_type anon_inode_fs_type = {
  	.name		= "anon_inodefs",
  	.get_sb		= anon_inodefs_get_sb,
  	.kill_sb	= kill_anon_super,
  };
  static struct dentry_operations anon_inodefs_dentry_operations = {
  	.d_delete	= anon_inodefs_delete_dentry,
  };
  
  /**

   * anon_inode_getfd - creates a new file instance by hooking it up to an

   *                    anonymous inode, and a dentry that describe the "class"
   *                    of the file
   *

   * @name:    [in]    name of the "class" of the new file

   * @fops:    [in]    file operations for the new file
   * @priv:    [in]    private data for the new file (will be file's private_data)
   * @flags:   [in]    flags

   *
   * Creates a new file by hooking it on a single inode. This is useful for files
   * that do not need to have a full-fledged inode in order to operate correctly.

   * All the files created with anon_inode_getfd() will share a single inode,

   * hence saving memory and avoiding code duplication for the file/inode/dentry

   * setup.  Returns new descriptor or -error.

   */

  int anon_inode_getfd(const char *name, const struct file_operations *fops,

  		     void *priv, int flags)

  {
  	struct qstr this;
  	struct dentry *dentry;

  	struct file *file;
  	int error, fd;
  
  	if (IS_ERR(anon_inode_inode))
  		return -ENODEV;

  	error = get_unused_fd_flags(flags);

  	if (error < 0)

  		return error;

  	fd = error;
  
  	/*
  	 * Link the inode to a directory entry by creating a unique name
  	 * using the inode sequence number.
  	 */
  	error = -ENOMEM;
  	this.name = name;
  	this.len = strlen(name);
  	this.hash = 0;
  	dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this);
  	if (!dentry)
  		goto err_put_unused_fd;

  
  	/*
  	 * We know the anon_inode inode count is always greater than zero,
  	 * so we can avoid doing an igrab() and we can use an open-coded
  	 * atomic_inc().
  	 */
  	atomic_inc(&anon_inode_inode->i_count);

  	dentry->d_op = &anon_inodefs_dentry_operations;
  	/* Do not publish this dentry inside the global dentry hash table */
  	dentry->d_flags &= ~DCACHE_UNHASHED;

  	d_instantiate(dentry, anon_inode_inode);

  	error = -ENFILE;
  	file = alloc_file(anon_inode_mnt, dentry,
  			  FMODE_READ | FMODE_WRITE, fops);
  	if (!file)
  		goto err_dput;

  	file->f_mapping = anon_inode_inode->i_mapping;

  
  	file->f_pos = 0;

  	file->f_flags = O_RDWR | (flags & O_NONBLOCK);

  	file->f_version = 0;
  	file->private_data = priv;
  
  	fd_install(fd, file);

  	return fd;

  err_dput:
  	dput(dentry);

  err_put_unused_fd:
  	put_unused_fd(fd);

  	return error;
  }

  EXPORT_SYMBOL_GPL(anon_inode_getfd);

  
  /*

   * A single inode exists for all anon_inode files. Contrary to pipes,
   * anon_inode inodes have no associated per-instance data, so we need
   * only allocate one of them.

   */
  static struct inode *anon_inode_mkinode(void)
  {
  	struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
  
  	if (!inode)
  		return ERR_PTR(-ENOMEM);
  
  	inode->i_fop = &anon_inode_fops;
  
  	/*
  	 * Mark the inode dirty from the very beginning,
  	 * that way it will never be moved to the dirty
  	 * list because mark_inode_dirty() will think
  	 * that it already _is_ on the dirty list.
  	 */
  	inode->i_state = I_DIRTY;
  	inode->i_mode = S_IRUSR | S_IWUSR;

  	inode->i_uid = current_fsuid();
  	inode->i_gid = current_fsgid();

  	inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
  	return inode;
  }
  
  static int __init anon_inode_init(void)
  {
  	int error;
  
  	error = register_filesystem(&anon_inode_fs_type);
  	if (error)
  		goto err_exit;
  	anon_inode_mnt = kern_mount(&anon_inode_fs_type);
  	if (IS_ERR(anon_inode_mnt)) {
  		error = PTR_ERR(anon_inode_mnt);
  		goto err_unregister_filesystem;
  	}
  	anon_inode_inode = anon_inode_mkinode();
  	if (IS_ERR(anon_inode_inode)) {
  		error = PTR_ERR(anon_inode_inode);
  		goto err_mntput;
  	}
  
  	return 0;
  
  err_mntput:
  	mntput(anon_inode_mnt);
  err_unregister_filesystem:
  	unregister_filesystem(&anon_inode_fs_type);
  err_exit:
  	panic(KERN_ERR "anon_inode_init() failed (%d)
  ", error);
  }
  
  fs_initcall(anon_inode_init);